The film starts with a young woman named Asha (Ariana DeBose) telling the tale of King Magnifico (Chris Pine). After witnessing sorrow and heartbreak in his life, Magnifico studied magic until he became a sorcerer and tried to use his gifts to provide for other people. Together with his wife, Queen Amaya (Angelique Cabral), they established the kingdom of Rosas. After everyone in the kingdom turns 18, they are able to give their wishes to Magnifico for the day he holds a wishing ceremony to grant their wishes.
Asha lives with her mother Sakina (Natasha Rothwell) and her grandfather Sabino (Victor Garber), plus pet goat Valentino. Sabino is turning 100, and the family hopes that he may be chosen to have his wish granted. Asha is also set to interview with Magnifico for a position as his apprentice. Asha then goes out to greet the people visiting Rosas (“Welcome To Rosas”) by telling them about the kingdom’s history and how great Magnifico is.
Asha goes to her best friend Dahlia (Jennifer Kumiyama), who is handicapped and also the kingdom’s baker. They are joined by the other teens in their group – grumpy Gabo (Harvey Guillen), sleepy Simon (Evan Peters), bashful Bazeema (Della Saba), happy Hal (Niko Vargas), sneezy Safi (Ramy Youssef), and dopey Dario (Jon Rudnitsky). They each give Asha advice on how to approach Magnifico, as well as having her be honest about her weaknesses.
Amaya arrives to escort Asha to meet with Magnifico. The king approaches Asha and remembers her late father. Magnifico then shows Asha his collection of the kingdom’s wishes (“At All Costs”), and she comes upon Sabino’s wish, which is to play music for the people in the kingdom. The moment that Asha asks if Sabino’s wish can be granted, Magnifico drops his friendly demeanor and claims that Sabino’s wish is too dangerous and may inspire a riot in the crowd. It is then revealed that when Magnifico takes the wishes, the people forget about the wish once it’s been given, and it removes a special part of their souls to make them dependent on Magnifico.
Magnifico later holds the wishing ceremony, using it as an attempt to be a jerk and deliberately not grant Sabino’s wish, while also not accepting Asha as his apprentice. She later has dinner with Sakina and Sabino, saying it’s her fault that their wishes will not be granted. When she tries to tell them what kind of king Magnifico really is, they do not believe her. Asha steps out with Valentino and makes a wish to the heavens (“This Wish”) for a way to help her family with their wishes. A great burst of light flashes through the sky, with everyone in the kingdom bearing witness. They initially all believe it is part of Magnifico’s magic, but even he is taken back by this power.
The Star that Asha wished on then comes down to the kingdom and starts to spread its magic on the animals and plants nearby, including Valentino (now voiced by Alan Tudyk). When Asha questions how any of this could happen, the animals join to explain (“I’m A Star”) that the magic from Star’s dust brought them to life. Asha then talks to Star, who non-verbally confirms that it cannot grant wishes, but does agree to help Asha and Valentino find her mother and grandfather’s wishes.
Asha brings Valentino and Star back to Magnifico’s castle as they try to find a way to sneak in quietly. Asha leaves them with some chickens before she runs into Dahlia and the other teens. They overhear Valentino and Star causing a commotion, which forces Asha to tell them the truth about what is going on and what she is trying to do. The teens help her find a way to sneak in while Star manages to find Sabino’s wish before Magnifico can catch them after Star accidentally causes a small fire.
The kingdom gathers outside Magnifico’s castle, only for him to address them and say the light they saw the night before did not come from him. He offers to grant the wish of anybody who has any information on whoever is responsible for the magic. Dahlia tries to stall Magnifico by asking him pressing questions, which causes the other subjects to question Magnifico, angering him. He retreats to his study to bemoan what is happening (“This is the Thanks I Get?!”) before going after a hidden spellbook that would allow him to use forbidden magic in his endeavors.
Asha returns home to show Sabino his wish. While he is at first overjoyed upon seeing it, their moment is ruined when Magnifico barges in, saying that someone turned Asha in. He holds Sakina’s wish and crushes it, which causes Sakina to experience intense grief while Magnifico discovers that absorbing wishes makes him even more powerful. Asha flees with her family (plus Valentino and Star) before sending Sakina and Sabino to a nearby island for safety while Asha tries to stop Magnifico.
Another gathering is held outside the castle as Magnifico announces a bounty on Asha, and then reveals that it was Simon who betrayed Asha, as he had been feeling left out of his friend group and wanted his wish granted. Magnifico then grants Simon’s wish, which is to become his most loyal knight. The wicked king then crafts a powerful staff and uses his magic to control Simon and make him betray the other six teens, forcing them to run and hide.
Asha runs into her friends, trying to explain to them that she did not do anything to harm them or the wishes of the people in the kingdom, and that Magnifico is evil. They believe her, and Amaya comes to join them after realizing her husband is beyond redemption (“Knowing What I Know Now”). They begin their plans to stop Magnifico.
Asha tries to lure Magnifico away from the castle while the teens and Valentino go to the room with the wishes to try and set them free. When it seems like Magnifico has caught up to Asha, it turns out to just be Simon having been disguised as Magnifico, and the villain is still at the castle. While the woodland creatures deal with Simon, Asha rides a horse back to the kingdom. Magnifico then holds the wishes back as the whole kingdom watches him reveal his true colors. With his staff, he captures Star and binds all of his subjects down using the power of their wishes. Asha makes it to the top of the tower to try and confront Magnifico, but his magic has become nearly unstoppable. When it seems as though Asha is defeated, she begins to inspire the rest of the subjects (“This Wish Reprise”), and the power from their hearts fuels their wish power. Star is freed, and the wishes are returned to the people, and for his failure, the forbidden magic imprisons Magnifico inside his staff.
The kingdom celebrates the return of their wishes, and Amaya, now sole queen of Rosas, has Magnifico’s little mirror prison be locked up in the dungeon, to his horror. Everyone is now able to make their own wishes come true. Simon also returns to apologize to Asha for what he did, and she and the other teens forgive him.
Another celebration is held, with Sabino finally being able to play music for everyone. Star makes it clear to Asha that it is time for it to return to the sky, but it gives Asha a magic wand to make her something of a fairy godmother to the people of Rosas. When her friends ask what they can do to help, Asha says they should just keep wishing. Fireworks then go off courtesy of Star, who creates the image of a certain famous mouse.
The credits feature star constellation images of every major Disney character since the beginning, from Mickey Mouse and Snow White to Wreck-It Ralph and Mirabel Madrigal. After the credits finish, the last thing we see is Sabino playing the tune of “When You Wish Upon a Star”.